I4 WATER FOR INDUSTRIAL PURPOSES ence of a few drops of methyl orange solution until a faint red coloration (similar to that given by methyl orange with a saturated solution of carbon dioxide in distilled water) is obtained. The result is expressed in grams of CaC03 per litre of the water; using 200 c.c. of the water, each i c.c. of the N/5-HC1 corresponds with 0-05 gram of CaCO-, per litre. When the water contains sodium carbonate—which is the case, not with ordinary natural waters, but only with certain mineral waters and with waters treated with sodium carbonate—it is necessary to boil a given volume of the water (gradually replacing that which evaporates) until the bicarbonates are decomposed, and then to filter and determine the alkalimetric titre of the filtrate. This alkalinity represents the sodium carbonate existing in the water, together with those minute quantities of the alkaline earth carbonates which remain dissolved (0-036 gram of CaC03 and o-i gram of MgC03 per litre).1 2. Determination of the Lime and Magnesia. Two hundred c.c. of the water are boiled for some minutes with excess of sodium carbonate solution in a porcelain dish and then evaporated to dryness. The residue is heated at 180° and treated with boiling water, the liquid being filtered and the precipitated alkaline earth carbonates washed with a little boiled water and dissolved in excess of N/5-hydrochloric acid. Tim excess of add is then titrated with. N/5-caustic soda, solution in presence of methyl orange. In this case, lime and magnesia, are calculated together as Cat); when 200 c.c. of the water are taken, each c.c. of N/5-HC1 used corresponds with 0-028 gram of CaO per litre of the water.- 3. Estimation of Sulphates .-—To 200 c.c. of the water, acidified with a little hydrochloric acid, barium chloride; is added ; if an appreciable precipitate forms after some hours, the sulphuric acid is estimated in the usual way (sec Potable Waters : Complete? Analysis, 4), The sulphuric acid found may be calculated as CaSO,,; i part of 'F»a,S()a corresponds with 0-5827 part of CaSO,,. 4. Other Tests.......-Where qualitative analysis shows the presence of marked quantities of magnesia, it is well to determine this gravimetneully, the lime being first eliminated by means of ammonium oxalate and the mag- nesia then precipitated with sodium phosphate and weighed as magnesium pyrophosphate in the ordinary way. i When an appreciable amount of chlorides is indicated qualitatively, the chlorine is determined (sec Potable Waters : Complete Analysis, 3) and calculated as NaCl. Also, if qualitative analysis reveals the presence of iron, this may be determined gravimetric-ally or colorimetrically by Lunge's method (see Aluminium Sulphate). 5. Calculation of the Results.—The lime (CaO) corresponding with the calcium sulphate found according to 3 is subtracted from the total lime found according to 2; the difference will represent the lime in the 1 The alkalinity of a water for industrial uses may also be determined "by the method indicated for Potable Waters: Partial Analysis, 3. 2 With waters rich in magnesia it is convenient to follow the method proposed by Wartha and Pfeifer (Zeitschr. /. angew. chem., 1902, p. 193) or that of Gigli (seep. $), taken for the titration of the excess of silver. ~, (.